Abstract

Wideband radar systems, especially those that operate at lower frequencies such as VHF and UHF, are often restricted from transmitting within or across specific frequency bands in order to prevent interference to other spectrum users. Herein we describe techniques for notching the transmitted spectrum of a generated and transmitted radar waveform. The notches are fully programmable as to their location, and techniques are given that control the characteristics of the notches.

@article{osti_1323319,
title = {Frequency-Dependent Blanking with Digital Linear Chirp Waveform Synthesis},
author = {Doerry, Armin Walter and Andrews, John M.},
abstractNote = {Wideband radar systems, especially those that operate at lower frequencies such as VHF and UHF, are often restricted from transmitting within or across specific frequency bands in order to prevent interference to other spectrum users. Herein we describe techniques for notching the transmitted spectrum of a generated and transmitted radar waveform. The notches are fully programmable as to their location, and techniques are given that control the characteristics of the notches.},
doi = {10.2172/1323319},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Tue Jul 01 00:00:00 EDT 2014},
month = {Tue Jul 01 00:00:00 EDT 2014}
}

This report analyzes the effects of finite-precision arithmetic on discrete Fourier transforms (DFTs) calculated using the chirp-z transform algorithm. An introduction to the chirp-z transform is given together with a description of how the chirp-z transform is implemented in hardware. Equations for the effects of chirp rate errors, starting frequency errors, and starting phase errors on the frequency spectrum of the chirp-z transform are derived. Finally, the maximum possible errors in the chirp rate, the starting frequencies, and starting phases are calculated and used to compute the worst case effects on the amplitude and phase spectrums of the chirp-z transform.more » 1 ref., 6 figs.« less

A digital system for controlling the mechanical tuning of a microwave cavity oscillator has been designed for use with accelerators. The microwave oscillator is used for driving the klystrons which provide the RF energy to accelerate the electrons to the desired energy. A logical system samples the electron beam pulse, which is at maximum amplitude when the microwave frequency is optimized. If the frequency drifts up or down, the system drives a dc stepping motor to which is geared the oscillator cavity and retunes the osciliator to the correct frequency. An additional feature built into the system provides the correctmore » startup operation (automatic frequency search) when the ac power is applied to the oscillator. To conserve development time and cost, the system design is based mainly on use of standard, commercially available, solid- state logic circuit modules. Modules designed by Lawrence Radiation Laboratory (LRL) are used where simplification is to be gained. The logic circuitry of the system based on these modules is described in detaii. (auth)« less

Definite advantages are gained by using a chirp (linear-FM) waveform for radar pulse compression. Digital generation of this waveform provides programmability, predictability, and repeatability. Of the digital implementations considered, the digital chirp synthesizer is shown to have the most flexibility and is more readily miniaturized than the arbitrary waveform generator design. Elements and features of the digital chirp synthesizer are examined and design considerations are presented. A TTL breadboard circuit that was built demonstrates the soundness of the fundamental design of the digital chirp synthesizer concept. 10 refs., 18 figs., 10 tabs.

Nonlinear FM (NLFM) waveforms offer a radar matched filter output with inherently low range sidelobes. This yields a 1-2 dB advantage in Signal-to-Noise Ratio over the output of a Linear FM (LFM) waveform with equivalent sidelobe filtering. This report presents details of processing NLFM waveforms in both range and Doppler dimensions, with special emphasis on compensating intra-pulse Doppler, often cited as a weakness of NLFM waveforms.